"Topological phases of static and driven systems" by Rahul Roy (UCLA)

Thursday, November 17, 2016 - 4:00pm to 5:00pm
Physics and Astronomy Colloquium

Thursdays, 4:00-5:00 pm

1-434 Physics and Astronomy (map)
Reception from 3:30-4:00 p.m.
(unless otherwise posted)

Guest Speaker: Rahul Roy (University of California, Los Angeles)

Talk Title:  “Topological phases of static and driven systems”


Topological ideas provide an approach to the identification and classification of phases that is altogether different from the conventional paradigm of spontaneous symmetry breaking. The integer and fractional quantum Hall effects, where the Hall conductance is often quantized to an accuracy greater than one part in a billion, are prominent examples of topological phases. These, and other such phases, cannot be distinguished by the types of order parameters that characterize symmetry broken phases, but are nevertheless distinct in their global topological properties and may be classified by a set of topological invariants. I will describe some of the early pioneering work on topological phases and invariants which was recognized by the 2016 Nobel Prize in physics awarded to D. J. Thouless, F. D. M. Haldane and J. M. Kosterlitz.  

I will go on to describe some recent developments in the field and focus in particular on efforts to classify topological phases of driven (Floquet) systems. A full classification of noninteracting fermionic Floquet systems has been obtained using K-theoretic methods. Topological phases of these systems exhibit robust edge modes reminiscent of the bulk-edge correspondence of  topological insulators. I will describe a set of newly discovered 2d interacting chiral drives, whose anomalous edge modes cannot be obtained from any 1d Hamiltonian and are robust to arbitrary small perturbations. Finally, I will describe a group cohomology construction of symmetry-protected Floquet phases in all dimensions, whose drives have the remarkable property of transforming trivial ground states at the boundary into topological ground states.

For more information, contact Jay Hauser

We thank the following people for their contributions to the wine fund for the post-colloquium reception:
Prof. Dolores Bozovic, Prof. Mike Cornwall, Prof. Bob Cousins, Prof. Andrea Ghez, Prof. Karoly Holczer, Prof. Eric Hudson, Robert Huff, Prof. Alex Kusenko, Prof. Myank Mehta, Prof. John Miao, Prof. Roberto Peccei, Prof. Claudio Pellegrini, Prof. David Saltzberg, Prof. Jean Turner and Prof. Ben Zuckerman.

1-434 PAB